1. Field of the Invention
This invention relates to a rotary stencil printing machine in which, in a series of sequential operations, a stencil sheet is wound on a printing drum while being thermally perforated by a thermal head according to a given original.
2. Description of Related Art
In the case where, in a series of sequential operations, e stencil sheet is thermally perforated by a thermal head to obtain a printing stencil, end wound on a printing drum, the following two methods are employed: In one of the methods, the stencil sheet is thermally perforated by a stencil making section, to obtain a printing stencil, and is then wound on the printing drum. In the other method, after the front end of the stencil sheet which is thermally perforated to obtain a printing stencil is locked to the printing drum with clamping means, only the stencil making operation is continued so that the part of the stencil sheet which is thermally perforated as was described above is temporarily held in a holding chamber. After the making of the printing stencil, the printing drum is turned to wind the stencil on it in one action.
The former method, however, suffers from a problem that the speed of conveyance of the stencil sheet in the stencil-making section must be equal to the speed at which the stencil sheet is wound on the printing the drum; otherwise the stencil sheet which is being thermally perforated by the stencil-making section is pulled, so that the picture formed on it with the thermal head may be deformed or broken, or the stencil sheet forms creases while being wound on the printing drum.
The later method has been proposed by Japanese Patent Application Laid-open No. Hei. 2-82566. The method is disadvantageous in that the direction in which the stencil sheet is slackened when conveyed out of the stencil-making section is not constant; that is, the stencil sheet, being bent irregularly, is liable to be broken. In addition, it has no means for regulating or absorbing the slackening of the stencil sheet, and therefore when the stencil sheet is wound on the printing drum, it is liable to be creased or damaged. Furthermore, the holding chamber, which adapted to temporarily hold the part of the stencil sheet which is thermally processed during the stencil making operation, must be large enough to hold even a long printing stencil. This requirement obstructs the miniaturization of the printing machine.